We are investigating the mental operations which take place in preparing to make skilled movement in order to gain insight into: l) the organization of normal motor programming; 2) the neural substrates mediating different components of the motor program, and 3) the pathophysiology of disorders of movement in neurologic patients. We will first demonstrate in normal individuals two separable components of the motor program: 1) conscious planning of a voluntary act through the activation, at a cortical level, of an abstract, sensorimotor memory (engram) of the intended act which can be prepared in response to a preliminary cue and held in a memory buffer before the release of; 2) a subcortical execution program specifying the spatiotemporal sequence of the intended act which is activated only after the signal to start the movement. We will then define the role of the basal ganglia in programming these components by studying unmedicated parkinson's patients and the effects of drug treatment. In a choice reaction time task subjects will write on a graphic tablet line sequences of varying length in response to target models displayed on a screen. Their ability to execute these drawings as a single program will be inferred from analysis of the timing of individual lines in the sequence and the pauses between them. Further, the generation of a motor program prior to the initiation of a movement will be inferred from an increase in reaction time to initiate sequences of increasing complexity. The components of this motor program will be dissociated by examining the effects of prior cueing (both valid and invalid) on reaction time. We anticipate an effect from prior cueing which will increase in magnitude and latency as function of sequence length; but that the slope of this function will not be different in the Parkinsonian state from the control condition when patients are on medication. We also anticipate that, even with valid cueing (which approaches a simple reaction time condition), there will remain a (smaller) increase in reaction time as a function of sequence length which represents the component of the motor program which can be activated only after a signal to execute the movement. We hope to implicate the basal ganglia as the neural substrate for this component by demonstrating an increase in the slope of this function for Parkinsonian state.